Contact lens having a uniform horizontal thickness profile

ABSTRACT

A contact lens having a rotational stabilization mechanism thereon, such as prism ballast, and a thickness profile that reduces the torque imparted on the lens by the action of the eyelids, especially for stabilizing toric lenses. The prism ballast is provided on one or more portions of the anterior face of the lens such that the lens body has a uniform thickness of within 10% along horizontal cross-sections. The anterior face of the lens may be segregated into a peripheral zone, an inner zone circumscribed by the peripheral zone, and a central optic zone. The prism ballast portion is provided within the inner zone, which may be further subdivided into a superior portion, an intermediate portion proximate the optic zone, and an inferior portion. The ballast portion increases in thickness along a superior-inferior line parallel to a vertical meridian, and has a substantially uniform thickness perpendicular thereto. The peripheral zone may be tapered, and have a rounded edge. The rate of thickness change across any portion of the peripheral zone is less than about 250 μm/mm.

RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C.§119(e) of U.S. provisional application No. 60/193,493, filed Mar. 31,2000.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to contact lenses and, inparticular, to an improved ballast, preferably a prism ballast, fortoric lenses that imposes a low-torque rotational correction on thelens.

[0003] Astigmatism is a defect in the eye that is corrected by a lenswith a non-spherical prescription. The prescription, which is usuallyexpressed as cylinder on the patient's prescription order, causes atleast a portion of the surface of the lens to have the shape of thetoric segment. A torus is a surface or object defined by the rotation ofa circle about an axis other than its own. For example, a donut has atoroidal shape. The toric portion of the lens is a small oval-shapedsection of the toroid, with a major axis and a minor axis. As a resultof this non-axi-symmetric configuration, proper rotational orientationof the lens must be maintained. It should be noted that other lenses,for instance that provide bifocal or multi-focal correction, arenon-axi-symmetric and thus have a particular orientation outside ofwhich performance suffers.

[0004] Astigmatism is often associated with other refractive errors suchas myopia or hypermetropia, and so toric contact lenses often alsoprovide some spherical correction, negative or positive. While theconcave or posterior surface of a contact lens generally has a sphericalconfiguration, where the lens is used to correct astigmatism theposterior surface will usually have the toric configuration. That is,the curved portion of the posterior surface of the lens has a major axisand a minor axis. The radius of curvature of the posterior surface ofthe lens is larger in the major-axis direction than in the minor-axisdirection. The major diameter of the toric surface is generally smallerin diameter than the overall lens, and is cut into a starting sphericalbase curve. Additionally, the anterior and/or posterior surface(s) ofthe optical zone may include a spherical portion that contributes to adistance refractive correction. The spherical correction is typicallyprovided on the exterior or anterior surface. Of course, certainprescriptions provide the toric curve on the anterior surface, with thespherical correction also on the anterior surface, or on the posteriorsurface.

[0005] While spectacle lenses are held rigidly in place by a frame,toric contact lenses must be stabilized so that the cylindricalcorrection is stabilized in substantially the correct position on theeye. Soft contact lenses which had been designed for use to correctastigmatism are well-known in the art. Generally, these lenses rely onsome type of ballasting or stabilizing method to cause the lens to beproperly oriented in the eye. The ballast is typically provided on acontact lens by incorporating structures either on the front surface oron the back surface, or spread between both surfaces. Such orientationstructures utilize eyelid forces generated during blinking. As theeyelids wipe across the contact lens, they tend to squeeze the lens downand against the cornea and displace elevated surface features.

[0006] A so-called “wedge” or “prism” ballast may be utilized whereinthe lower or inferior portion of the lens is relatively thicker than theupper or superior portion. As a result, the upper eyelid, whichundergoes greater movement than the lower eyelid, and thus exertsgreater influence on the contact lens, tends to displace the inferiorportion of the contact lens downward, inherently rotating the contactlens over the cornea into the intended orientation. Alternatively, thelens may incorporate a so-called “periballast” (short for peripheralballast) stabilization that involves a ballast region surrounding butexcluding the central optic.

[0007] For examples of prism ballast, see U.S. Pat. Nos. 4,573,774,5,125,728, and 5,020,898, and PCT Publication No. WO 98/45749. Anotherorientation structure for contact lenses includes the provision of thinsuperior and inferior zones relative to a thicker central zone. Suchstructures are shown in U.S. Pat. Nos. 4,095,878, and 5,650,837.Alternatively, channels or ridges may be provided on the contact lens,such as seen in PCT publication No. AU 92/00290.

[0008] U.S. Pat. No. 5,020,898 describes a toric contact lens withballast distributed outside the anterior optical zone such that theballast thickens from the top of the lens to two points of maximumthickness proximate the lower peripheral edge.

[0009] U.S. Pat. No. 5,125,728 also describes a ballast portion thatincreases from a superior part of the lens to a maximum thickness in thelower periphery on each side thereof. The maximum thickness of theballast is located as close as possible to the lens edge so that theseportions fit over the peripheral cornea and conjunctiva to limit lensrotation. A ballast-free corridor of least resistance is provided in thevertical mid-section of the lens above and below the central opticalarea. The patent asserts that the ballast-free corridor in combinationwith the thicker ballast and thicker portions close to the lensperiphery provides an improved stabilization mechanism.

[0010] Finally, PCT Publication No. WO 98/45749 describes a ballast lenswith a prism through the optical zone. The anterior and posterioroptical zone diameters are selected such that when combined to form alens, the thickness at the superior and inferior junctions of theoptical zone on the anterior face is controlled.

[0011] In addition to the relative ability of a lens to orientconsistently on cornea, other factors affect the performance of thevarious stabilization structures. For example, some structures arebetter than others with respect to one or more of the following:reducing the overall thickness across the toric contact lens for thephysiological benefit of the wearer, ease of manufacture, reducing thelens parameter inventory, clinical performance including wearer comfortand consistency of fitting between refractive powers. With respect towearer comfort, in general, the thinner the lens and the smoother thesurface, the more comfort will be provided. In addition, it is known toprovide a periphery on the lens that is relatively thin and shaped foradded comfort.

[0012] The principal limitation of existing toric contact lens designsis that orientation is highly variable and/or uncomfortable, for a givendesign, between individual toric lens wearers. Besides the lens designand lens material, patient factors also influence the orientation of atoric contact lens on the eye and contribute to this variability in lensorientation. Patient factors such as blink characteristics and ocularparameters such as eyelid, corneal, and conjuctival shape and anatomymay result in undesired interaction (for example, asymmetry) orinsufficient interaction with the contact lens. However, many of theproblems associated with prior art mechanisms may be attributed toproblems with failure of the stabilization mechanism to maximize eyelidinteraction and reduce the variability of lens orientation betweenindividuals.

[0013] Despite much effort in this area, there is still a need for atoric contact lens that has more consistent stabilization featuresbetween individuals.

SUMMARY OF THE INVENTION

[0014] In accordance with the present invention, a contact lens havingimproved thickness and ballast arrangement is provided. The contact lensof the present invention reduces the known variability of lensorientation from individual to individual. Further, the lenses of thepresent invention provide more effective interaction between thestabilization mechanism and the eyelid during blinking, and preferablyinclude a peripheral zone that is required for wearer comfort.

[0015] In one aspect, therefore, the present invention provides acontact lens, including a contact lens body having a generally sphericalbase curvature with a convex anterior face, a concave posterior face,and a peripheral edge therebetween. A peripheral zone is definedadjacent the peripheral edge of the anterior face. The body has athickness between the anterior face and the posterior face and isnon-axi-symmetric so as to define a superior edge and an inferior edge.Further, a vertical meridian is defined from the superior edge towardthe inferior edge and a horizontal meridian is defined perpendicularthereto. The anterior face defines a plurality of zones thereon,including an inner zone circumscribed by the peripheral zone, and anoptic zone defined generally in the middle of the inner zone.Additionally, the lens includes a prism ballast portion whereby thethickness increases parallel to the vertical meridian from the superioredge toward the inferior edge in at least a ballast portion of the innerzone. The inner zone comprises a superior portion between the optic zoneand the superior extent of the inner zone, an inferior portion betweenthe optic zone and the inferior extent of the inner zone, and anintermediate portion between the superior and inferior portions. Theballast portion is defined within one or more of the superior,intermediate, and inferior portions and has a series of consecutivehorizontal cross-sections exclusive of the peripheral zone and opticzone spanning a distance along the vertical meridian of at least 20% ofthe smallest dimension of the superior, intermediate, and inferiorportions as measured along the vertical meridian, wherein eachhorizontal cross-section has a substantially uniform thickness notvarying by more than about 30 μm or 20%, whichever is greater inabsolute terms. In one embodiment, the thickness of the contact lens ineach of the consecutive horizontal cross-sections does not vary by morethan about 15 μm or about 10%, whichever is greater in absolute terms.

[0016] In one embodiment, the ballast portion is defined wholly withinonly one of the superior, intermediate, and inferior portions. Inanother embodiment, the ballast portion is defined wholly within onlytwo of the superior, intermediate, and inferior portions. In stillanother embodiment, the ballast portion is defined within all three ofthe superior, intermediate, and inferior portions, or comprises theentire inner zone.

[0017] In a preferred embodiment, a rate of change of thickness in thetapered peripheral zone is less than about 250 μm/mm, more preferablyless than about 200 μm/mm.

[0018] In an alternative embodiment, a contact lens of the presentinvention comprises a contact lens body having a generally sphericalbase curvature with a convex anterior face, a concave posterior face,and a peripheral edge therebetween. A peripheral zone is definedadjacent the peripheral edge of the lens that tapers thinner toward theperipheral edge of the lens. The lens body has a thickness between theanterior face and the posterior face and is non-axi-symmetric so as todefine a superior edge and an inferior edge. A vertical meridian isdefined from the superior edge toward the inferior edge and a horizontalmeridian is defined perpendicular thereto. The anterior face defines aplurality of zones thereon, including an inner zone circumscribed by theperipheral zone and having a prism ballast portion therein, and an opticzone defined generally in the middle of the inner zone, wherein the isthickness increases parallel to the vertical meridian from the superioredge toward the inferior edge in at least the prism ballast portion ofthe inner zone. Along a 225° meridian, the distance between the innerzone and the peripheral edge is less than about 1.4 mm.

[0019] In accordance with one aspect of the invention, a molded contactlens includes a fully molded contact lens body (i.e., molded on both theanterior and posterior faces) having the general features as describedabove. As before, the molded lens has a prism ballast portion in theinner zone and, along a 225° meridian, the distance between the innerzone and the peripheral edge is less than about 1.8 mm. Alternatively,or desirably in addition, and along a 270° meridian, the distancebetween the inner zone and the peripheral edge is less than about 2.1mm, while along a 180° meridian, the distance between the inner zone andthe peripheral edge is less than about 1.3 mm.

[0020] Desirably, a band circumscribed by the peripheral zone and aroundthe optic zone is substantially annular.

[0021] Namely, a superior distance A is defined along the verticalmeridian and within the inner zone from the optic zone to the peripheralzone. An inferior distance B is defined along the vertical meridian andwithin the inner zone from the optic zone to the peripheral zone. Formolded prism ballasted lenses the band is annular within the range of0.33A≦B≦A, while for all prism ballasted lenses the annular band iswithin the range of 0.55A≦B≦A.

[0022] Each and every feature described herein, and each and everycombination of two or more of such features, is included within thescope of the present invention provided that the features included insuch a combination are not mutually inconsistent.

[0023] The invention, together with additional features and advantagesthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying illustrativedrawings in which like parts bear like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic front elevational view of a contact lensaccording to the present invention illustrating various zones definedthereon;

[0025]FIG. 2 (A-A′ to E-E′) illustrate a series of horizontalcross-sections taken through the lens of FIG. 1;

[0026]FIG. 3 is a graph showing the varying thickness of the contactlens of FIG. 1 taken along a vertical meridian Z-Z′;

[0027]FIG. 4a is a schematic diagram of the contact lens of the presentinvention having an exemplary topographical numerical thickness mapsuperimposed thereon;

[0028]FIG. 4b is a graph of a portion of the contact lens of the presentinvention illustrating a discontinuity and angular relationship betweenzones thereon;

[0029]FIGS. 5a-5 d are elevational views of contact lenses of thepresent invention each having a spherical anterior optical zone andvarying regions of substantially uniform horizontal thickness;

[0030]FIGS. 6a-6 d are elevational views of contact lenses of thepresent invention each having a toric anterior optical zone and varyingregions of substantially uniform horizontal thickness;

[0031]FIG. 7 is a schematic front elevational view of a contact lenshaving a number of meridian lines superimposed thereon for reference;and

[0032]FIG. 8 is a schematic front elevational view of a contact lens ofthe prior art illustrating various zones defined thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present invention provides stabilized contact lenses,especially contact lenses having a cylindrical correction forastigmatism. More broadly, the present invention provides contact lenseshaving elevated surfaces thereon that interact with the blinking actionof the eyelids to rotationally stabilize the lens. The rotationalstability is useful for any contact lens that is non-axi-symmetric. Forexample, the rotational orientation of toric lenses or multifocal lensesmust be maintained for proper correction. It should be understood,however, that rotational stability may also be desirable for otherspecialized lenses.

[0034] In the following description, a number of surfaces andthicknesses of the contact lenses of the present invention will bedescribed with reference to schematic elevational views of the lenses,in that the lenses have been flattened. Contact lenses typically possessan underlying spherical curvature, with the anterior face being convex,and the posterior face being concave. The various surfaces and opticzones are then either molded or machined from the base sphere. Forsimplicity, the elevational views shown herein are flattened, with thebase sphere removed. In this way, the lines of shading corresponding tothe underlying spherical curvature are removed so that the particularsurfaces and thicknesses of the present invention can be more clearlyillustrated. In a preferred embodiment, lenses of the present inventionhave a negative spherical power distance correction, and a toric surfacefor cylindrical correction.

[0035] An exemplary contact lens 20 of the present invention is thusshown in schematic elevational view in FIG. 1 flattened without shadingto illustrate various zones thereon. The lens 20 includes a lens body ofsuitable soft or rigid material. Soft contact lenses are typically madeof a hydrophilic material such as hydroxyethylmethacrylate,metallo-organic substances, silicone rubbers, silicone hydrogels,urethanes, etc. Alternatively, a rigid gas-permeable material such assiloxane acrylate or fluorosiloxane acrylate may be used. The lens bodyhas an overall spherical curvature with a concave posterior face adaptedto contact the cornea opposite an outwardly-facing concave anteriorface.

[0036] With reference to FIG. 1, the lens 20 includes an optic zone 22,a peripheral zone 24, and an inner zone 26 circumscribed by theperipheral zone, wherein the optic zone 22 forms a portion of the innerzone 26. Alternatively, the inner zone 26 may be defined between theoptic zone and the peripheral zone. As will be described further herein,the optic zone 22 may be circular, toroidal, or other special shapes.The peripheral zone 24 may have a uniform radial dimension (width), orthe radial dimension may vary. In the exemplary illustrated embodiment,the peripheral zone 24 has a narrower radial dimension at a superior end30, and a wider radial dimension at an inferior end 32. Stated anotherway, the inner zone 26 has a circular periphery or ballast periphery 34that is slightly offset toward the top of the lens 20 along a verticalmeridian or centerline Z-Z′ therethrough. It should be noted that theclear delineations in the drawings between the optic zone 22 peripheralzone 24 and inner zone 26 should not be taken to imply that there is adiscontinuity or corner at those locations, and in fact the exemplarylens of the present invention possesses gradually curved transitionsbetween the zones.

[0037] A lens edge 36 defines the intersection of the anterior andposterior faces. The peripheral zone 24 desirably exhibits a taper so asto be thinner at the lens edge 36 than at the circular ballast periphery34. In this regard, the peripheral zone 24 preferably defines a partialconical surface (albeit, superimposed on the underlying sphericalcurvature). Alternatively, the peripheral zone 24 may define a partialspherical or other curvature (i.e., shape), for example, any suitablecurvature.

[0038] Various features of the lens 20 are believed to enhance wearercomfort in comparison to other similar lenses. Indeed, certain clinicaltrials resulted in findings that patients responded more favorably toquestions designed to ascertain a comfort level of lenses made accordingto the present invention than with respect to questions on the comfortlevel of similar lenses.

[0039] The inner zone 26 may be segregated into three parts along thevertical meridian Z-Z′. Specifically, a superior portion 40 extendsbetween the upper extent of the ballast periphery 34 and the upperextent of the optic zone 22, delineated by an imaginary line 42,perpendicular to the vertical meridian Z-Z′. An intermediate portion 44extends between the perpendicular line 42 and a second perpendicularline 46 at the lower extent of the optic zone 22. Finally, an inferiorportion 48 extends between the perpendicular line 46 and the lowerextent of the ballast periphery 34. The optic zone 22 thus lies entirelywithin the intermediate portion 44.

[0040] The superior portion 40, intermediate portion 44, and inferiorportion 48 are used in the present application to segregate the innerzone 26 into discrete areas in which specific ballast surfaces can beprovided. It should be understood, however, that the dividing lines 42,46 between the areas may be shifted, or may be non-linear, for thatmatter. In one aspect, the present invention concerns particular ballastor prism ballast surfaces/thicknesses in one or more portions of theinner zone 26, which portions may be defined in a number of ways.Therefore, the reader will understand that the portions 40, 44, and 48are shown as exemplary only. Desirably, iso-thickness ballast surfacesare formed in at least 20% (measured as a percent of the verticaldimension), preferably at least 50%, and more preferably at least 100%,of at least one of the portions 40, 44, and 48. More specifically, aniso-thickness prism ballast portion is defined within one or more of thesuperior, intermediate, and inferior portions 40, 44, and 48 as a seriesof consecutive horizontal cross-sections-exclusive of the peripheralzone and optic zone spanning a distance along the vertical meridian ofat least 20% of the smallest dimension of the superior, intermediate,and inferior portions as measured along the vertical meridian. The term“iso-thickness” means that each of the consecutive horizontalcross-sections has a substantially uniform thickness not varying by morethan about 30 μm or 20%, whichever is greater in absolute terms. In aparticularly preferred construction, ballast surfaces are provided in atleast two, more preferably all three of the portions 40, 44, and 48.

[0041] The present invention pertains to contact lenses havingrotational stabilization mechanisms thereon, including those withballasts, e.g., prism ballasts, periballasts, and so-called “dynamicallystabilized” lenses. A ballasted lens provides some raised surfacecontour over which the eyelid wipes to re-orient the lens, generallyabout its optical axis. A prism ballast provides a wedge or taperedballast for interaction with the eyelids even in the optic, while aperiballast is exclusive of the optic. Dynamic stabilization involvessuperior and inferior flats on the lens leaving a thickened midsectionto interact with the eye, as seen in U.S. Pat. No. 4,095,878. Those ofskill in the art will also recognize that there may be other suchstabilization mechanisms with which the present invention could beadvantageously used.

[0042]FIG. 1 also illustrates a number of representative cross-sectionallines A-A′, B-B′, C-C′, D-D′, and E-E′ extending perpendicularly withrespect to the vertical meridian Z-Z′ (i.e., horizontally). Thesesections are illustrated in FIG. 2, with the base spherical curvatureshown. The present invention provides that consecutive horizontalcross-sections shown in FIG. 2 that possesses ballast each has asubstantially uniform or iso-thickness, except in the optic zone 22 andperipheral zone 24. For example, one of the cross-sections in FIG. 2having ballast, such as D-D′, has a substantially uniform thickness.Alternatively, all of the cross sections shown in FIG. 2 that possessballast may have a uniform thickness except in the optic zone 22 andperipheral zone 24.

[0043] Desirably, the sections of substantially uniform thickness do notvary in thickness within one section by more than about 30 μm or about20% whichever is greater in absolute terms. In one embodiment, thethickness of the sections varies by no more than about 15 μm or about10%, such as by no more than about 10 μm or about 7%, whichever isgreater. Such variations will be understood to be sufficiently smallthat the sections can still be regarded as being of “substantiallyuniform” thickness.

[0044] In an exemplary embodiment of the present invention, the contactlens 20 has a so-called prism ballast superimposed thereon within theentire inner zone 26. That is, from the intersection of the ballastperiphery 34 with the vertical meridian Z-Z′ at the top of the lens 20,to the intersection between the same two lines at the bottom of thelens, the thickness generally increases. This thickness distributionalong the vertical meridian Z-Z′ is graphically illustrated in FIG. 3,with the superior end 30 of the peripheral zone 24 shown at the rightand the inferior end 32 shown at the left. Starting at the right side,the taper of the peripheral zone 24 within the superior end 30 from theedge 36 to the upper extent of the ballast periphery 34 is seen. In thesuperior portion 40, the thickness gradually increases to the horizontalline 42. The thickness further increases through the optic zone 22 tothe horizontal line 46. The greatest thickness is in the inferiorportion 48 to the lower extent of the ballast periphery 34. The lensagain tapers downward within the peripheral zone 24 between the ballastperiphery 34 to the inferior edge 36.

[0045] The thickness distribution represented in FIG. 3 thus correspondsto a prism ballast within the lens 20 that extends through all of thesuperior portion 40, intermediate portion 44, and inferior portion 48.Indeed, even the optic zone 22 exhibits this prism ballast. Importantly,the present invention provides a prism ballast in at least one of theseportions 40, 44, 48 having horizontal cross-sections of uniformthickness. Therefore, as seen in FIG. 2, all of the cross-sectionsillustrated have uniform thicknesses along their widths, except in theperipheral zone 24. Of course, because of the increasing thickness inthe superior-inferior direction parallel to the vertical meridian Z-Z′,the thickness of each cross-section increases from cross-section A-A′ tocross-section E-E′.

[0046] The uniform thickness in the horizontal cross-sections helps tostabilize lenses of the present invention, in contrast to previouslenses. More specifically, lenses of the present invention are suitablefor a greater number of wearers than those of the prior art because ofthe lower torque exerted by the eyelids on the lens by virtue of theuniform thickness or iso-thickness configuration. The iso-thicknessballast arrangement maximizes eyelid interaction by achieving an evencontact across each section of the lens as the eyelid travels down andup the lens during blinking. In contrast, the eyelid generates morerotational torque during a normal blink when interacting with horizontallens sections of non-uniform thickness, as in the prior art. This isbecause for a lens to orient appropriately on the eye the lens-eyelidinteraction should be maximized across the lens (i.e., across eachhorizontal cross-section) so that the lens is squeezed into the desiredorientation (overall orientation) and undergoes minimal fluctuationduring blinking (interblink orientation).

[0047] Prior art lenses, having narrow peaks or points of maximumthickness on either side of the vertical meridian are more likely tocreate a non-uniform lens-eyelid interaction across horizontal sections.In addition, the horizontal distance between peaks of maximum thicknessin the prior art lenses typically increases from a superior portion tothe horizontal midline, and then decreases from the mid-line to theinferior portion. This further varies the lens-eyelid interactionforces.

[0048] The uniform thicknesses in the horizontal cross-sections of thelens 20 have proven to enhance performance of the lenses in comparisonto other similar lenses in terms of maintaining a correct rotationalorientation in the eye. Clinical trials have shown that there is lessvariability in the position of a location mark on the lens over time.For example, groups of 20 people at a time were studied to determine thepositions of location marks over time on various lenses in the eye, andthe standard deviations of the positions of the location marks weredetermined. The results are that the standard deviation for lenses ofthe present invention are measurably smaller than in other lenses,meaning the present lenses had less rotational instability in the eye.

[0049] Exemplary values for the thickness of the contact lens 20 havingthe distribution as seen in FIG. 3 are provided in the topographicaldepiction of FIG. 4a. It is understood that the contact lens 20 shown inFIG. 4a is generally circular. In FIG. 4a, the inner zone 26 is dividedby—horizontal and vertical grid lines into a plurality of discreteunits. Each horizontal row of units has a uniform thickness throughoutthe inner zone 26. On the other hand, the thickness along a verticalcolumn of units generally increases from the superior to the inferior.For example, horizontal row 50 has a uniform thickness of 140 μm otherthan in the optic zone. Vertical column 52 has a thickness of 70 μm atthe top, gradually increases to 280 μm, and begins to decrease justprior to the inferior portion of the peripheral zone 24. The valuesprovided in FIG. 4a are exemplary and are suitable for a soft hydrogelcontact lens. The values for lenses made of other materials may varydepending on the optical or other properties of the particular material.

[0050] It will be understood by the reader that the discrete unitsmapped in FIG. 4a represent the average thickness within each unit. Thatis, the thickness down the lens 20 changes gradually, rather than at astepped border between units. More generally, although the presentapplication describes distinct zones or portions in contact lenses,those zones are shown for clarity of description of the invention only.It will be appreciated by those skilled in the art that there are nosharp distinctions between these different zones of the lens, but thatthey are instead smoothly blended into one another.

[0051]FIG. 4a also illustrates the decreasing thickness or taper of thelens 20 through the peripheral zone 24. For example, at the inferiormidpoint, the thickness decreases from 210-140-70 μm. This is also seenin the graph of FIG. 3. This taper within the peripheral zone 24provides a so-called comfort zone around the edge of the lens 20.Because of the reduced thickness, movement of the eyelids across thecontact lens is facilitated, and there is less irritation. Specifically,the eyelids more easily travel over the tapered peripheral zone 24 thanif there were a more abrupt thickness change.

[0052] In an exemplary embodiment, the lens 20 has a corneal fittingrelationship to maintain the lens centered on the cornea. The preferredlens has a diameter sufficient to achieve corneal coverage, and optimumstability is provided so that the lens does not become loose andunstable with gaze and blinking, which may influence the comfort andvision of the wearer. The sagittal depth (concave depth of the posteriorface) for an optimum lens-cornea fitting relationship is between about3.0 and 5.0 mm over a lens diameter of between about 13.0 mm and 16.0mm. The lens diameter is more preferably between about 13.5-14.8 mm. Apreferred thickness of the lens edge 36 is less than about 120 μm, morepreferably about 90 μm. In this respect, the thickness is measuredradially with respect to the curvature of the anterior face. The extremeoutermost extent of the edge 36 may incorporate a preferred rounding ofthe anterior edge corner.

[0053] A plurality of meridian lines may be defined through the centerof the lens. In a preferred embodiment, for maximum wearer comfort, therate of change in lens radial thickness from the end of the ballast zone34 to the lens edge 36 (i.e., in the peripheral zone 24) is less thanabout 250 μm/mm along any meridian of the lens. For example, in thetopographical map of FIG. 4a, the rate of change of thickness along anymeridian and within the peripheral zone 24 is less than about 250 μm/mm.More preferably, the rate of change in the peripheral zone 24 is lessthan about 200 μm/mm.

[0054] The advantageous interaction between the peripheral zone 24 andthe iso-thickness is further exemplified in the proximity to the lensedge 36 of the point of maximum thickness, as variously measured aroundthe lens. To illustrate this principle, FIG. 7 shows various meridiansthrough the optical axis and around the lens in degrees, starting at the3:00 o'clock position and moving counterclockwise. Of course, withiso-thickness in the inner zone 26, the point of maximum thickness alongany horizontal meridian corresponds to the thickness along the entirehorizontal meridian excluding the optical zone. Therefore, the beginningof the inner zone 26 and the point of maximum thickness along anymeridian always lies on the ballast periphery 34. However, because ofthe preferred ballasting, the maximum thickness changes around theballast periphery 34.

[0055] For prism ballasted lenses in accordance with the presentinvention, and along the 225° meridian, the distance between the pointof maximum thickness (e.g., the ballast periphery 34) and the lens edge36 is no greater than about 1.4 mm, regardless of the thickness. For anytype of ballasted lens, the maximum thickness along the 225° meridian inaccordance with the present invention is between about 200-4000 μm,preferably between about 250-350 μm, and more preferably about 320 μm.Along the 270° meridian, the distance between the point of maximumthickness (e.g., the ballast periphery 34) and the lens edge 36 is nogreater than 1.8 mm, also regardless of the thickness, though athickness of about 320 μm is preferred. For fully molded prism ballastedlenses (i.e., molded on both the anterior and posterior faces), andalong a 225° meridian, the distance between the between the point ofmaximum thickness (e.g., the ballast periphery 34) and the peripheraledge is less than about 1.8 mm, and desirably, along a 270° meridian,the distance between the point of maximum thickness and the peripheraledge is less than about 2.1 mm. Also, along a 180° meridian, thedistance between the inner zone and the peripheral edge is less thanabout 1.3 mm. In general, the peripheral zone 24 of the lenses of thepresent invention are relatively narrow in comparison to the prior artballasted lenses, yet because of the preferred thicknesses the comforttaper angle in the peripheral zone 24 is relatively shallow, asmentioned above.

[0056] Although the preferred lens of the present invention has smooth,rounded transitions between different portions thereon, discreteboundaries or corners are not excluded. For example, the transitionbetween the peripheral zone 24 and the inner zone 26 may be defined by arounded corner or discontinuity at the circular ballast periphery 34. Anexample of the transition between the ballast area 26 and the peripheralzone 24 (i.e., at 34) along the meridian Z-Z′ is seen in FIG. 3.

[0057]FIGS. 5a-5 d illustrate several variations of the contact lens ofthe present invention having different ballast portions defined withinthe ballast zone. For purpose of explanation, the reader will refer backto FIG. 1 for the definition of the various portions (i.e., superior,intermediate, and inferior) of the inner zone 26. FIG. 5a shows acontact lens 70 having a ballast portion 72 defined within the superiorportion of the inner zone. Again, the inner zone lies between an opticzone 74 and a peripheral zone 76. FIG. 5b illustrates a contact lens 80of the present invention having a ballast portion 82 defined within boththe superior and intermediate portions of the inner zone. FIG. 5c showsa contact lens 90 having a ballast portion 92 defined within the entireinner zone, through the superior, intermediate, and inferior portionsthereof. Finally, FIG. 5d illustrate a contact lens 100 having a ballastportion 102 defined only within the inferior portion of the inner zone.

[0058] Other variations not shown include a ballast portion definedwholly within either the intermediate or inferior portions of the innerzone, or within the intermediate and inferior portions combined,exclusive of the superior portion. Also, the ballast portion couldsurround the optic zone in a so-called “periballast” arrangement, orcould continue through the optic zone in a so-called “prism ballast”arrangement.

[0059]FIGS. 6a-6 d illustrate a number of other contact lenses of thepresent invention having a cylindrical correction on the anterior facethereof. More specifically, a toric optic zone 110 is shown in each ofthe lenses oriented along a major axis 112 that is rotated with respectto the superior-inferior axis of the lens. The need for properballasting for the lenses is thus apparent to maintain the proper offsetorientation of the axis 112.

[0060]FIG. 6a shows a contact lens 120 having a ballast portion 122beginning in the superior portion and continuing through both theintermediate and inferior portions of the inner zone. FIG. 6b shows acontact lens 130 having a ballast portion 132 located entirely withinthe inferior portion of the inner zone. FIG. 6c depicts a contact lens140 having a ballast portion 142 wholly within the intermediate portionof the inner zone. Finally, FIG. 6d shows a lens 150 having a ballastportion 152 only within the superior portion of the inner zone.

[0061]FIG. 8 shows a prism ballast lens of the prior art (CooperVisionFrequency Xcel (Encore) Toric) with lines demarking the transitionsbetween various zones drawn. Specifically, an optic zone 200 isseparated from a ballast zone 202 by a generally circular inner line204, and the ballast zone is separated from a peripheral zone 206 by agenerally circular outer line 208. While the inner line 204 isapproximately centered as expected on the optical axis OA, the outerline 208 is offset upward along the vertical meridian 210. As a result,the ballast zone 202 is wider in the superior region than the inferior.Specifically, the superior radial width A of the ballast zone 202 issignificantly greater than the inferior radial width B. Indeed, thesuperior radial width A is more than twice the inferior radial width B.

[0062] In contrast, as seen in FIG. 1, the lenses of the presentinvention have an inner zone 26 that is substantially annular, with aradial dimension A that is within about 300% of the radial width B. Thatis, for molded prism ballasted lenses the band is annular and therelationship 0.33A≦B≦A holds. Alternatively, for all prism ballastedlenses the annular band is within the range of 0.55A≦B≦A.

[0063] It will be appreciated that the present invention may be embodiedin lenses having varying optical powers. For example, a contact lens ofpresent invention may have an optic power of about between about −8 toabout +8 diopters, although this range is not to be considered limiting.

[0064] Additionally, the contact lenses according to the presentinvention may also comprise stabilization features other than theuniform thickness ballast arrangement. For example, the peripheral zonemay include a flattened region for dynamic stabilization, or the lensmay incorporate a periballast stabilization outside of the centraloptic.

[0065] While this invention has been described with respect to variousspecific examples and embodiments, it is to be understood that theinvention is not limited thereto and that it can be variously practicedwithin the scope of the following claims.

What is claimed is:
 1. A contact lens, comprising: a contact lens bodyhaving a generally spherical base curvature with a convex anterior face,a concave posterior face, and a peripheral edge therebetween with aperipheral zone being defined adjacent the peripheral edge of theanterior face that is tapered thinner toward the peripheral edge of thelens, the body having a thickness between the anterior face and theposterior face and being non-axi-symmetric so as to define a superioredge and an inferior edge, with a vertical meridian being defined fromthe superior edge toward the inferior edge and a horizontal meridianbeing defined perpendicular thereto; a plurality of zones on theanterior face, including an inner zone circumscribed by the peripheralzone, and an optic zone defined generally in the middle of the innerzone, wherein the inner zone includes a ballast portion and thethickness increases parallel to the vertical meridian from the superioredge toward the inferior edge in at least the ballast portion of theinner zone; wherein the inner zone comprises a superior portion betweenthe optic zone and the superior extent of the inner zone, an inferiorportion between the optic zone and the inferior extent of the innerzone, and an intermediate portion between the superior and inferiorportions; and the ballast portion is defined within one or more of thesuperior, intermediate, and inferior portions and has a series ofconsecutive horizontal cross-sections exclusive of the peripheral zoneand optic zone spanning a distance along the vertical meridian of atleast 20% of the smallest dimension of the superior, intermediate, andinferior portions as measured along the vertical meridian, wherein eachhorizontal cross-section has a substantially uniform thickness notvarying by more than about 30 μm or 20%, whichever is greater inabsolute terms.
 2. The contact lens of claim 1, wherein the thickness ofthe at least one horizontal cross-section does not vary by more thanabout 15 μm or 10%, whichever is greater in absolute terms.
 3. Thecontact lens of claim 1, wherein, along a 225° meridian, the distancebetween the inner zone and the peripheral edge is less than about 1.45mm.
 4. The contact lens of claim 1, wherein, along a 225° meridian, arate of change of thickness in the tapered peripheral zone is less thanabout 250 μm/mm.
 5. The contact lens of claim 1, wherein the ballastportion is a prism ballast.
 6. The contact lens of claim 1, wherein theballast portion spans a distance along the vertical meridian of at least50% of the smallest dimension of the superior, intermediate, andinferior portions as measured along the vertical meridian.
 7. Thecontact lens of claim 1, wherein the ballast portion is defined whollywithin only one of the superior, intermediate, and inferior portions. 8.The contact lens of claim 1, wherein the ballast portion is definedwholly within only two of the superior, intermediate, and inferiorportions.
 9. The contact lens of claim 1, wherein the ballast portion isdefined within all three of the superior, intermediate, and inferiorportions.
 10. The contact lens of claim 1, wherein the ballast portionspans a distance along the vertical meridian of at least 50% of therespective dimensions of the superior, intermediate, and inferiorportions as measured along the vertical meridian.
 11. The contact lensof claim 10, wherein the ballast portion spans a distance along thevertical meridian of at least 100% of the respective dimensions of thesuperior, intermediate, and inferior portions as measured along thevertical meridian.
 12. The contact lens of claim 11, wherein the ballastportion is provided on the entire inner zone including the optic zone.13. The contact lens of claim 11, wherein the ballast portion isprovided on the entire inner zone except for the optic zone.
 14. Thecontact lens of claim 1, further including a cylindrical correction oneither the anterior face or the posterior face.
 15. The contact lens ofclaim 14, wherein the cylindrical correction is provided on theposterior face, and wherein the optic zone of the anterior facecomprises a spherical correction.
 16. The contact lens of claim 1,wherein the inner zone is of substantially uniform radial width aroundthe circumference of the lens.
 17. The contact lens of claim 16, whereina band circumscribed by the peripheral zone and around the optic zone issubstantially annular, with a superior distance A being defined alongthe vertical meridian and within the inner zone from the optic zone tothe peripheral zone, and an inferior distance B being defined along thevertical meridian and within the inner zone from the optic zone to theperipheral zone, and wherein 0.25A≦B≦A.
 18. The contact lens of claim 1,wherein the body is a soft contact lens.
 19. The contact lens of claim1, wherein the ballast portion is a periballast.
 20. The contact lens ofclaim 1, wherein the lens further incorporates a dynamic stabilizationmechanism.
 21. The contact lens of claim 1, wherein the lens furtherincorporates a negative spherical power distance correction.
 22. Acontact lens, comprising: a contact lens body having a generallyspherical base curvature with a convex anterior face, a concaveposterior face, and a peripheral edge therebetween with a peripheralzone being defined adjacent the peripheral edge of the lens that tapersthinner toward the peripheral edge of the lens, the body having athickness between the anterior face and the posterior face and beingnon-axi-symmetric so as to define a superior edge and an inferior edge,with a vertical meridian being defined from the superior edge toward theinferior edge and a horizontal meridian being defined perpendicularthereto; wherein the anterior face defines a plurality of zones thereon,including an inner zone circumscribed by the peripheral zone and havinga prism ballast portion therein, and an optic zone defined generally inthe middle of the inner zone, wherein the thickness increases parallelto the vertical meridian from the superior edge toward the inferior edgein at least the prism ballast portion of the inner zone; and wherein,along a 225° meridian, the distance between the inner zone and theperipheral edge is less than about 1.4 mm.
 23. The contact lens of claim22, wherein, along the 225° meridian, a rate of change of thickness inthe tapered peripheral zone is less than about 250 μm/mm.
 24. Thecontact lens of claim 23, wherein, along the 225° meridian, a rate ofchange of thickness in the tapered peripheral zone is less than about200 μm/mm.
 25. The contact lens of claim 22, wherein the maximumthickness along a 225° meridian of the lens is between about 200-400 μm.26. The contact lens of claim 25, wherein the maximum thickness alongthe 225° meridian is between about 250-350 μm.
 27. The contact lens ofclaim 22, wherein the inner zone comprises a superior portion betweenthe optic zone and the superior extent of the inner zone, an inferiorportion between the optic zone and the inferior extent of the innerzone, and an intermediate portion between the superior and inferiorportions, and wherein the prism ballast portion is defined within one ormore of the superior, intermediate, and inferior portions and has aseries of consecutive horizontal cross-sections exclusive of theperipheral zone and optic zone spanning a distance along the verticalmeridian of at least 20% of the smallest dimension of the superior,intermediate, and inferior portions as measured along the verticalmeridian, wherein each horizontal cross-section has a substantiallyuniform thickness not varying by more than about 30 μm or 20%, whicheveris greater in absolute terms.
 28. The contact lens of claim 22, wherein,along a 270° meridian, the distance between the inner zone and theperipheral edge is less than about 1.8 mm.
 29. A molded contact lens,comprising: a fully molded contact lens body having a generallyspherical base curvature with a convex anterior face, a concaveposterior face, and a peripheral edge therebetween with a peripheralzone being defined adjacent the peripheral edge of the lens that tapersthinner toward the peripheral edge of the lens, the body having athickness between the anterior face and the posterior face and beingnon-axi-symmetric so as to define a superior edge and an inferior edge,with a vertical meridian being defined from the superior edge toward theinferior edge and a horizontal meridian being defined perpendicularthereto; wherein the anterior face defines a plurality of zones thereon,including an inner zone circumscribed by the peripheral zone and havinga prism ballast portion therein, and an optic zone defined generally inthe middle of the inner zone, wherein the thickness increases parallelto the vertical meridian from the superior edge toward the inferior edgein at least the prism ballast portion of the inner zone; and wherein,along a 225° meridian, the distance between the inner zone and theperipheral edge is less than about 1.8 mm.
 30. The contact lens of claim29, wherein the maximum thickness along the 225° meridian is betweenabout 200-400 μm.
 31. The contact lens of claim 29, wherein the innerzone comprises a superior portion between the optic zone and thesuperior extent of the inner zone, an inferior portion between the opticzone and the inferior extent of the inner zone, and an intermediateportion between the superior and inferior portions, and wherein theprism ballast portion is defined within one or more of the superior,intermediate, and inferior portions and has a series of consecutivehorizontal cross-sections exclusive of the peripheral zone and opticzone spanning a distance along the vertical meridian of at least 20% ofthe smallest dimension of the superior, intermediate, and inferiorportions as measured along the vertical meridian, wherein eachhorizontal cross-section has a substantially uniform thickness notvarying by more than about 30 m or 20%, whichever is greater in absoluteterms.
 32. The contact lens of claim 29, wherein, along a 270° meridian,the distance between the inner zone and the peripheral edge is less thanabout 2.1 mm.
 33. The contact lens of claim 29, along a 180° meridian,the distance between the inner zone and the peripheral edge is less thanabout 1.3 mm.
 34. A molded contact lens, comprising: a fully moldedcontact lens body having a generally spherical base curvature with aconvex anterior face, a concave posterior face, and a peripheral edgetherebetween with a peripheral zone being defined adjacent theperipheral edge of the lens that tapers thinner toward the peripheraledge of the lens, the body having a thickness between the anterior faceand the posterior face and being non-axi-symmetric so as to define asuperior edge and an inferior edge, with a vertical meridian beingdefined from the superior edge toward the inferior edge and a horizontalmeridian being defined perpendicular thereto; wherein the anterior facedefines a plurality of zones thereon, including an inner zonecircumscribed by the peripheral zone and having a prism ballast portiontherein, and an optic zone defined generally in the middle of the innerzone, wherein the thickness increases parallel to the vertical meridianfrom the superior edge toward the inferior edge in at least the prismballast portion of the inner zone; and wherein, along a 180° meridian,the distance between the inner zone and the peripheral edge is less thanabout 1.3 mm.
 35. The contact lens of claim 34, wherein, along a 270°meridian, the distance between the inner zone and the peripheral edge isless than about 2.1 mm.
 36. The contact lens of claim 34, wherein theinner zone comprises a superior portion between the optic zone and thesuperior extent of the inner zone, an inferior portion between the opticzone and the inferior extent of the inner zone, and an intermediateportion between the superior and inferior portions, and wherein theprism ballast portion is defined within one or more of the superior,intermediate, and inferior portions and has a series of consecutivehorizontal cross-sections exclusive of the peripheral zone and opticzone spanning a distance along the vertical meridian of at least 20% ofthe smallest dimension of the superior, intermediate, and inferiorportions as measured along the vertical meridian, wherein eachhorizontal cross-section has a substantially uniform thickness notvarying by more than about 30 μm or 20%, whichever is greater inabsolute terms.
 37. A contact lens, comprising: a contact lens bodyhaving a generally spherical base curvature with a convex anterior face,a concave posterior face, and a peripheral edge therebetween with aperipheral zone being defined adjacent the peripheral edge of the lensthat tapers thinner toward the peripheral edge of the lens, the bodyhaving a thickness between the anterior face and the posterior face andbeing non-axi-symmetric so as to define a superior edge and an inferioredge, with a vertical meridian being defined from the superior edgetoward the inferior edge and a horizontal meridian being definedperpendicular thereto; wherein the anterior face defines a plurality ofzones thereon, including an inner zone circumscribed by the peripheralzone and having a ballast portion therein, and an optic zone definedgenerally in the middle of the inner zone, wherein the thicknessincreases parallel to the vertical meridian from the superior edgetoward the inferior edge in at least the ballast portion of the innerzone; and wherein a band circumscribed by the peripheral zone and aroundthe optic zone is substantially annular, with a superior distance Abeing defined along the vertical meridian and within the inner zone fromthe optic zone to the peripheral zone, and an inferior distance B beingdefined along the vertical meridian and within the inner zone from theoptic zone to the peripheral zone, and wherein 0.55A≦B≦A.
 38. A moldedcontact lens, comprising: a contact lens body having a generallyspherical base curvature with a convex anterior face, a concaveposterior face, and a peripheral edge therebetween with a peripheralzone being defined adjacent the peripheral edge of the lens that tapersthinner toward the peripheral edge of the lens, the body having athickness between the anterior face and the posterior face and beingnon-axi-symmetric so as to define a superior edge and an inferior edge,with a vertical meridian being defined from the superior edge toward theinferior edge and a horizontal meridian being defined perpendicularthereto; wherein the anterior face defines a plurality of zones thereon,including an inner zone circumscribed by the peripheral zone and havinga molded prism ballast portion therein, and an optic zone definedgenerally in the middle of the inner zone, wherein the thicknessincreases parallel to the vertical meridian from the superior edgetoward the inferior edge in at least the ballast portion of the innerzone; and wherein a band circumscribed by the peripheral zone and aroundthe optic zone is substantially annular, with a superior distance Abeing defined along the vertical meridian and within the inner zone fromthe optic zone to the peripheral zone, and an inferior distance B beingdefined along the vertical meridian and within the inner zone from theoptic zone to the peripheral zone, and wherein 0.33A≦B≦A.